Fix computation of length of LTL formulas.

* src/ltlvisit/length.cc: Fix computation for ltl::multop
operator. "a&b&c" was reported with length 3, ignoring the
"&" operators, because of a typo.
* src/ltlvisit/length.hh: Fix description to correctly
reflect this change intended since 2010-01-22.
* src/ltltest/length.test, src/ltltest/length.cc: New files.
* src/ltltest/Makefile.am: Add them.

src/ltltest/length.test

@@ -0,0 +1,29 @@
+#! /bin/sh
+# Copyright (C) 2012 Laboratoire de Recherche et Developpement
+# de l'Epita (LRDE).
+#
+# This file is part of Spot, a model checking library.
+#
+# Spot is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# Spot is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+# or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+# License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with Spot; see the file COPYING.  If not, write to the Free
+# Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA.
+
+
+. ./defs || exit 1
+
+set -e
+
+test `run 0 ../length 'a U Xc'` = 4
+test `run 0 ../length 'a&b&c'` = 5
+test `run 0 ../length 'a|b|c'` = 5